Update ReactNativeZoomableView.js

[kristijantomic]

handles double tap to zoom to center of the the view

[SimonErich]

Thank you very much for your MR @kristijantomic .
Unfortunately I couldn't merge it directly, because I think zooming to center is not the default expected behavior of this.
I took your code however and implemented it with a new propery called doubleTapZoomToCenter that will take care of that.

So now you can have that exact behavior, but just have to use the doubleTapZoomToCenter prop on your component.